1. Field of the Invention
The invention relates to reflectors for electromagnetic radiation and in particular, though to exclusively, to radar reflectors for enhancing the radar cross-section of an object.
2. Discussion of Prior Art
GB Patent Application No. 2194391A describes a reflector comprising a spherical lens, having a dielectric constant of substantially equal to 3.414 with a reflective coating formed over a part of the spherical surface of the lens. Electromagnetic radiation, e.g. radar, is focussed by the lens on to the reflector and then reflected back towards the radar source. When suitably designed with the reflector covering about one half of the lens a highly uniform radar cross section covering substantially a hemisphere of angles of incidence resulted. This meant that two lenses, back-to-back, could provide a substantially uniform radar cross-section, independent of the direction of incidence of the radiation. Such reflectors provide a simpler and cheaper alternative to Luneberg lenses and their uniform response makes them suitable for use, for example, on top of yacht masts to provide suitably large echoes on ships' radar scanners to mimimise the likelihood of collisions.
The invention provided a material with the correct dielectric constant and low loss transmission characteristics. However the weight of the reflector is a critical factor in various applications and a compromise was needed between maximising the radar cross-section and mimimising the weight.